Heart failure is a condition in which a patient's heart works less efficiently than it should, a condition in which the heart fails to supply the body sufficiently with the oxygen rich blood it requires, either at exercise or at rest. Congestive heart failure (CHF) is heart failure accompanied by a build-up of fluid pressure in the pulmonary blood vessels that drain the lungs. Transudation of fluid from the pulmonary veins into the pulmonary interstitial spaces, and eventually into the alveolar air spaces, is called pulmonary edema, and can cause shortness of breath, hypoxemia, acidosis, respiratory arrest, and death.
It is estimated that about four million people in the United States suffer from various degrees of heart failure. Although CHF is a chronic condition, the disease often requires acute hospital care. Patients are commonly admitted for acute pulmonary congestion accompanied by serious or severe shortness of breath. Acute care for congestive heart failure accounts for the use of more hospital days than any other cardiac diagnosis, and consumes in excess of seven and one-half billion dollars in the United States annually.
It is far more cost effective, and much better for the patient's health, if chronic CHF can be managed and controlled by the routine administration of appropriate drug therapy rather than by hospital treatment upon the manifestation of acute symptoms. Patients with chronic CHF are typically placed on triple or quadruple drug therapy to manage the disease. The drug regimen commonly includes diuretics, vasodilators such as ACE inhibitors or A2 receptor inhibitors, and inotropic agents usually in the form of cardiac glycosides such as Digoxin. Patients may also be placed on beta blockers such as Carvedilol.
As with all drugs, these agents must be taken in doses sufficient to ensure their effectiveness. Problematically, however, over-treatment can lead to hypotension, renal impairment, hyponatremia, hypokalemia, worsening CHF, impaired mental functioning, and other adverse conditions. Adding to the challenge of maintaining proper drug dosage is the fact that the optimal dosage will depend on diet, particularly salt and fluid intake, level of exertion, and other variable factors. Adding further to the problem of managing this condition is the fact that patients frequently miss scheduled doses by forgetting to take pills on time, running out of medications, or deciding to stop medications without consulting their physician. It is important, therefore, that the patient's condition be monitored regularly and thoroughly, so that optimal or near optimal drug therapy can be maintained. This monitoring is itself problematic, however, in that it requires frequent visits with a caregiver, resulting in considerable inconvenience and expense.
It would be highly advantageous, therefore, if methods and apparatus could be devised by which a patient's congestive heart failure could be monitored routinely or continuously with minimal attendance by a caregiver, and then only when actually required. It would be further advantageous if such methods and apparatus included means for communicating diagnostic information not only to the physician but to the patient himself, so that the patient could continue or modify his own drug therapy appropriately and generally without the direct intervention of a physician. The present invention provides these very advantages, along with others that will be further understood and appreciated by reference to the written disclosure, figures, and claims included in this document.